radio squeal question.

[Stealth Pilot]

radio is an icom a200
headset is a clone of a dave clark, an australian altronics C9073

when taxying and early into the flight when I press the ptt the radio
squeals in the headset.
after a while in the air the squeal vanishes and the radio setup works
just fine.

I changed headsets today while taxying out and discovered that the
squeal vanished with the headset. The new/different headset worked
fine.

I thought it might have been moisture/condensation and have wd40'd the
connectors without changing the problem one iota.

anyone an idea as to what would cause this problem?
all equipment appears to be in sound working order with no damage.

Stealth Pilot

[RST Engineering]

My best guess is that the "cloners" didn't take into account RF pickup by
the headset leads and you are getting RF into the mic circuit, which
rectifies in the first transistor junction it comes to, becomes an audio
signal, feeds itself into the transmitter modulator, gets on the output,
feeds itself into the headset leads, and round and round we go.

Jim


"Stealth Pilot" > wrote in message
...
>
> radio is an icom a200
> headset is a clone of a dave clark

[User]

RST Engineering wrote:
> My best guess is that the "cloners" didn't take into account RF pickup by
> the headset leads and you are getting RF into the mic circuit, which
> rectifies in the first transistor junction it comes to, becomes an audio
> signal, feeds itself into the transmitter modulator, gets on the output,
> feeds itself into the headset leads, and round and round we go.
>
> Jim
>
>
> "Stealth Pilot" > wrote in message
> ...
>> radio is an icom a200
>> headset is a clone of a dave clark
>
>
Ahh Jim You are correct... a lot of problems with Altronic headsets due
shielding etc.... Some of our customers have fitted ferrite beads on
the headset line and that seems to work well.
Australian or otherwise, they are NOT a David Clarke !! and fall well
short as a clone.

Regards Michael @ XCOM

[Stealth Pilot]

On Mon, 06 Nov 2006 02:26:25 GMT, USER > wrote:

>RST Engineering wrote:
>> My best guess is that the "cloners" didn't take into account RF pickup by
>> the headset leads and you are getting RF into the mic circuit, which
>> rectifies in the first transistor junction it comes to, becomes an audio
>> signal, feeds itself into the transmitter modulator, gets on the output,
>> feeds itself into the headset leads, and round and round we go.
>>
>> Jim

thanks jim. it hasnt been evident for 6 years. I wonder why it clears
after some flying time. hmmm.....whats about to fail....

>>
>>
>> "Stealth Pilot" > wrote in message
>> ...
>>> radio is an icom a200
>>> headset is a clone of a dave clark
>>
>>
>Ahh Jim You are correct... a lot of problems with Altronic headsets due
>shielding etc.... Some of our customers have fitted ferrite beads on
>the headset line and that seems to work well.
>Australian or otherwise, they are NOT a David Clarke !! and fall well
>short as a clone.
>
>Regards Michael @ XCOM

interesting comments. they have been in use in the aircraft for 6
years without problem up until recently so i suspect that your
comments are not quite correct.
a friend and I have flown in his thorp and swapped the dave clarks and
the altronics for 15 minutes about. neither of us could tell the
difference. we dont believe that they fall short as a clone.

the latest dave clarks at $aus1,350 or so a headset are more expensive
than gold for the weight if my calc was correct.

Stealth Pilot

[User]

The latest David Clarks don't compare to the Altronics... the DC 13.4's
do and they are only $480 AU$... the latest DC's have all the bells and
whistles (and the price tag).

All i can do is speak from experience having 1200 XCOM customers, many
in AU with Altronics headsets and a vast majority cause problems.....

Simple test, press the PTT button with one set of headsets only plugged
in and move around the cockpit, does the squealing sound change ??
turn your head in all sorts of directions and listen to the squeal
change, this is RF feedback getting into the headsets. If it was the
wiring in the aircraft it doesn't move and the squeal would be more or
less the same. Please try the test.

Now why after 6 years is this suddenly happening ?? It could be the
shielding has finally let go from pulling the plugs out by the cords, it
could be tarnishing on the plugs it could be a heap of things... even
corrosion on your aerial.

Send me an email through XCOM for some more ideas or call me on 0418 168
665 if you need any other help.

Regards Michael @ XCOM

Stealth Pilot wrote:
> On Mon, 06 Nov 2006 02:26:25 GMT, USER > wrote:
>
>> RST Engineering wrote:
>>> My best guess is that the "cloners" didn't take into account RF pickup by
>>> the headset leads and you are getting RF into the mic circuit, which
>>> rectifies in the first transistor junction it comes to, becomes an audio
>>> signal, feeds itself into the transmitter modulator, gets on the output,
>>> feeds itself into the headset leads, and round and round we go.


>>> Jim
>
> thanks jim. it hasnt been evident for 6 years. I wonder why it clears
> after some flying time. hmmm.....whats about to fail....
>
>>>
>>> "Stealth Pilot" > wrote in message
>>> ...
>>>> radio is an icom a200
>>>> headset is a clone of a dave clark
>>>
>> Ahh Jim You are correct... a lot of problems with Altronic headsets due
>> shielding etc.... Some of our customers have fitted ferrite beads on
>> the headset line and that seems to work well.
>> Australian or otherwise, they are NOT a David Clarke !! and fall well
>> short as a clone.
>>
>> Regards Michael @ XCOM
>
> interesting comments. they have been in use in the aircraft for 6
> years without problem up until recently so i suspect that your
> comments are not quite correct.
> a friend and I have flown in his thorp and swapped the dave clarks and
> the altronics for 15 minutes about. neither of us could tell the
> difference. we dont believe that they fall short as a clone.
>
> the latest dave clarks at $aus1,350 or so a headset are more expensive
> than gold for the weight if my calc was correct.
>
> Stealth Pilot
>
>

[ELIPPSE]

Stealth Pilot wrote:
> radio is an icom a200
> headset is a clone of a dave clark, an australian altronics C9073
>
> when taxying and early into the flight when I press the ptt the radio
> squeals in the headset.
> after a while in the air the squeal vanishes and the radio setup works
> just fine.
>
> I changed headsets today while taxying out and discovered that the
> squeal vanished with the headset. The new/different headset worked
> fine.
>
> I thought it might have been moisture/condensation and have wd40'd the
> connectors without changing the problem one iota.
>
> anyone an idea as to what would cause this problem?
> all equipment appears to be in sound working order with no damage.
When you are on the ground the antenna pattern is modified by the
nearby ground, allowing more of the RF field to be incident on your
headset and wiring. Sometimes, also, if your antenna is on the bottom,
the nearby ground can change your antenna's SWR, which may result in
antenna currents flowing on the outside of the coax. You might try
ferrite beads on your mic leads close to where they enter the radio,
and also a large clamp-on ferrite on your antenna's coax near the
antenna connection.
>
> Stealth Pilot